Process for forming composite aluminum alloy



nited tates 3,436,804 PROCESS FOR FORMING COMPQSlTE ALUMINUM ALLOY IrwinBroverman, Orange, Conn., assignor to Olin Mathieson ChemicalCorporation, a corporation of Virginia No Drawing. Continuation ofapplication Ser. No. 288,870, June 19, 1963. This application Apr. 23,1968, Ser. No. 723,629

Int. Cl. B23k 31/02, 1/20 U.S. Cl. 29-4715 6 Claims This application isa continuation of now abandoned application Ser. No. 288,870 filed onJune 19, 1963.

The present invention relates to a new and improved process for forminga composite aluminum alloy and to the resultant composite. Moreparticularly, the present invention resides in a novel, convenient andexpedient process for forming a composite aluminum alloy which combineshigh strength with good bright anodizing characteristics.

It is highly desirable to provide aluminum alloys which combine goodbright anodizing characteristics and high strength. The term brightanodizing is used herein in the conventional sense, that is, a finishingprocess consisting of, for example, optional buffing and polishing ofthe work piece, chemical brightening by, for example, a nitric acid typesolution, anodizing in an electrolyte, such as sulfuric acid and sealingin hot water containing the conventional additives, if desired.

The commercially available aluminum alloys that are capable of providinghigh quality, high specular finish upon bright anodizing are generallyrelatively low strength alloys. The base-purity of such alloys isrelatively high and the total alloying content relatively small. Thefollowing table shows typical commercial alloys amenable to brightanodizing. In the following table, and throughout the presentspecification, the alloy designations are those assigned by the AluminumAssociation.

TABLE 1 Composition, percent Alloy Si (max.) Fe (maxi) Cu (max.) Mn Mg0. l2 0. 17 O. 07 0. 15-0. 45 0. 8-1. 2 O. 08 0.10 O. 20 0. l0v 45 0.8-1. 2 0.10 0.12 0.15 0.10-0.40 0.4-0. 8 0 08 0. l0 0. 10 0. 03-max. 0.20-0. 60

Typical yield strength for the foregoing group of alloys in the fullyannealed condition ranges from about 5000 p.s.i. for alloy 5257, thelast alloyed material, to about 7000 p.s.i. for alloy 5357, thestrongest of the group. At the present time, the bright anodized finishobtainable with alloy 5457 is a standard generally accepted by thealuminum finishing industry.

Heretofore, it has been found possible to increase the magnesium contentof the aluminum base alloy to about 2.5 percent, thereby effectivelyincreasing the strength and yet maintaining bright anodizingcharacteristics comparable with those of alloy 5457. A yield strength ofabout 12,000 p.s.i. in the fully annealed condition is obtained in suchan alloy. However, when the magnesium content is increased beyond 2.5percent in order to further strengthen the material, it is found thatthe brightness, clarity and specularity of the bright anodizing finishare depreciated significantly, unless the impurity content issignificantly lowered.

In order to overcome these limitations and, in fact, optimally toachieve even higher strength properties, it has been suggested to clad ahigh strength core material with a good bright anodizing coatingmaterial; however, when a high strength aluminum base alloy containingfrom 2 to 10 percent magnesium is heated, there is formed on the surfacea harmful layer of surface oxide that is enriched in magnesium oxide.This layer makes the forge welding of the cladding layer to the core orbacking extremely difiicult or erratic. One method which has beensuggested to overcome this difficulty is to include varying amounts ofan additional alloying ingredient, such as beryllium in an amount up toabout 0.5 percent, in the core material. While this eflectivelyovercomes the difficulty, it is subject to the disadvantages ofrequiring additional and often undesirable alloying ingredients.

Other methods for overcoming these limitations include (l) the use of acontrolled atmosphere for heating of the cladding and core materialsprior to the forge welding operation, and also (2) compounds, such assodium fiuoborate may be added to the furnace atmosphere to reduce theoxide formation. These methods are expensive and may require specialequipment.

Accordingly, it is an object of the present invention to provide a noveland convenient process for achieving a composite aluminum alloycombining high strength with good bright anodizing characteristics.

It is a further object of the present invention to provide a process asaforesaid for cladding a high strength aluminum alloy core material witha good bright anodizing aluminum coating.

It is a still further object of the present invention to provide aprocess as aforesaid which is simple, convenient and readily amenable tocommercial practices.

It is an additional object of the present invention to provide a processas aforesaid which enables the formation of new and improved highstrength, good bright anodizing aluminum alloy composites without thenecessity of utilizing undesirable or expensive or inconvenient alloyingmaterials.

Further objects and advantages of the present invention will appearhereinafter.

In accordance with the present invention it has now been found that theforegoing objects and advantages can be readily and convenientlyaccomplished and there is obtained a novel clad product, i.e., acomposite alloy, and a method for cladding a core material. Thecomposite alloy comprises an aluminum base alloy containing from 2 to 10percent magnesium with a coating consisting essentially of aluminum, andthe method comprises forming an assembly by superimposing said coatingon said core, venting the air at the interface and integrating said coreand said coating.

The process of the present invention results in a high strength, goodbright anodizing aluminum composite which achieves numerous heretoforeunobtainable and often surprising advantages. These advantages will bediscussed and elaborated upon throughout the present specification andexamples. Surprisingly, the characteristics of the composite in thefully annealed condition are: a minimum yield strength of 14,000 p.s.i.,a minimum tensile strength of 35,000 p.s.i. and a minimum elonga tion of15 percent in two inches. In addition, surprisingly, the brightanodizing characteristics of the resultant composite are at least asgood as, and generally superior to, those of the cladding alloy insingle form.

The alloy obtained in accordance with the process of the presentinvention is especially useful in the preparation of formed articlessince it has the characteristics necessary for use therein, such as goodformability and fine grain size control.

-It has been further found, surprisingly and unexpectedly, that thepresent invention renders it readily possible to produce sound, highstrength bonds by hot rolling a high strength aluminum-magnesium coreand good bright anodizing aluminum-magnesium surface cladding. This isquite surprising in view of the simple process employed in the presentinvention and in view of the common belief TABLE 2 Content, percentAlloy Mg Mn Or 5086 4. 0. 45 0. 15 5083 4. 0. G5 0. 15 5456 5. 1 0. 750. l5 Undesignated 7. 0

The typical yield strength in the fully annealed condition of the abovealloys ranges from 17,000 p.s.i. for alloy 5086 to 21,000 p.s.i. foralloy 5083 and to 23,000 p.s.i. for alloy 5456. The correspondingtensile strengths of these alloys are typically 38,000 p.s.i. for alloy5086', 42,000 p.s.i. for alloy 50 83 and 45,000 p.s.i. for alloy 5456.

The core material may, of course, be any conventional high strengthaluminum base alloy containing from 2 to percent magnesium andpreferably at least 85 percent aluminum. Additional alloying ingredientsmay, of course, be added to the core material if desired in order toobtain particular characteristics, as, for example, manganese andchromium may be added to obtain additional strength and provide bettergrain size control. The use of undesirable alloying ingredients is notnecessary in accordance with the present invention in order to obtain agood bond between the core material and the coating material. Typi caland conventional alloying elements often used and compatible inaccordance with the present invention include the following withrepresentative ranges thereof: manganese, from 0.15 to 1.0 percent, andchromium from .05 to .30 percent.

The cladding material which may be employed consists essentially ofaluminum, i.e. a good bright anodizing material, such as an aluminumalloy containing up to 2.5 percent magnesium, and preferably from 0.01to 2.5 percent, or alternatively, high purity or super purity aluminum.Where an aluminum base alloy is employed the aluminum content ispreferably at least 95 percent. Conventional additives or other alloyingmaterials may, of course, be included in the cladding material, providedthat the good bright anodizing characteristics are not impaired, forexample, any of the following or mixtures thereof: copper, up to 0.3percent; manganese, up to 0.45 percent; iron, up to 0.17 percent;silicon, up to 0.12 percent; i.e., from about 0.001 up to the upperfigure given. Typical coating alloys are those listed in Table 1 above.

The optimum cladding thickness is dependent upon the final buflingrequirements. Generally speaking, it is not desirable to employ coatingsabove 20 percent since the thicker the coating the less the effect ofthe high strength core material is felt, and preferably from 5 to 20percent.

In the preferred operation, the mating surfaces are cleaned in theconventional manner, such as chemical cleaning and wire brushing. Thecore material does not need to be hot worked prior to assembly with thecladding material for the hot rolling operation. The cladding issuperimposed on the core to form an assembly, and the assembly isperipherally integrated leaving an unintegrated peripheral portion inthe posterior section of said assembly, e.g., the core material isfusion welded to the coating material around its entire peripheryleaving an unwelded area in one portion thereof. This unwelded area orexit vent serves to permit the escape of entrapped air or magnesiumoxide. Once this is done the composite or assembly may be hot rolled bycommercial rolling equipment with entrapped air escaping through theexit 4 vent. The cladding material is generally hot rolled to therequired gauge that will give the necessary percentage of the thicknessof the final composite. Heating of the assembly for rolling may be donein a natural air atmosphere.

Alternatively, but less desirable, the initial fusion Welding may beomitted and the core and coating material superimposed to form acomposite, followed by an ironing pass" at slow speed, i.e., less thanabout 10 feet per minute in the absence of rolling lubricant and with areduction on the order of about less than 10 percent. This ironing passserves to exhaust entrapped air by pressure, brings the cladding andcore materials into intimate contact, i.e., a partial mechanical bond,and effectively precludes the contamination of the interface by rollinglubricant during the subsequent reduction to achieve a sound pressureweld. Subsequent passes may then fully weld the components.

In the preferred operation a minimum hot rolling reduction of about 30percent is preferred prior to further hot rolling to final gauge.

In accordance with the present invention good bonds were obtained at hotrolling temperatures ranging from 450 to 950 F.

The resultant pressure welded interface of the composite alloy ischaracterized by no bond blistering developing during the thermaltreatments of the composite alloy including high temperature annealingand no separation at the interface during extreme bending or drawing andcupping tests in which the pressure weld was held. In addition, thetensile properties of the composite alloy at 0.040 to 0.050 inch gaugewere virtually equal to those of the core alloys in single alloy formdespite a surface cladding of 8.5 percent of the much softer brightanodizing alloy. This characteristic is quite surprising and unexpectedand means, in effect, for all practical purposes, the mechanicalproperties of the core alloys may be used to approximate the strengthand formability. This is a particular and useful advantage of thepresent invention. Therefore, the composite alloy is characterized bythe apparent strength of the core material and the bright anodizingcharacteristics of the cladding material.

Still further, the bright anodizing characteristics of the claddingalloy, including brightness, clarity, specularity and freedom fromtextural and structural streaking were noticeably improved as comparedwith the same alloy in single form produced by normal productionmethods. This improvement prevailed throughout the entire temperaturerange of hot rolling.

Other and significant advantages of the present invention include theattainment of good bright anodizing characteristics in the conventionalbright anodizing alloy with a Wide latitude of control in thefabricating operations. These cladding alloys were not as sensitive tothe effects of thermal treatment as they normally are in the singleform. In addition, fine grain size control was readily achieved in thecomposite.

The present invention and improvements resulting therefrom will be morereadily apparent from a consideration of the following illustrativeexamples.

Example 1.--Core alloy 5086claddin-g alloy 5457 The above core andcladding alloys were used in samples 9 inches long, 6 inches wide and1.125 inches thick for alloy 5086 and 0.125 inch thick for alloy 5457.The mating surfaces of the alloys were cleaned and were brushed. Thecladding alloy was superimposed on the core alloy to form an assemblyand then sandwich welded along the entire lead end, sides and tail,except for a small vent in the tail end. The composite was then hotrolled by a light pass at 30 feet per minute followed by heavy passes atfeet per minute. The temperatures ranged from 850 F. to 500 F. The finalgauge of half of the samples was 0.250 inch, and half 0.150 inch. Thesamples were then cold rolled and annealed. The bright anodizingcharacteristics of the resultant composite were visually observed to besuperior to those of the cladding alloy in single form in respect tospecularity, clarity and uniformity.

The resultant composites had the following characteristics:

Yield strength p.s.i. 17,000-20,000 Tensile strength p.s.i.36,000-38,000 Elongation in two inches percent 21-27 Additionalcharacteristics of the composite were: the high ductility of thecomposite, as evidenced by the large volume of elongation in the tensiletest, in combination with the high strength levels imparted by the corematerial, enabled severe forming operations to be accommodated; thegrain size of the cladding in the composite was observed to be generallyfiner than the same material in single alloy form; the integrity andsoundness of the bonding between the core alloy and the cladding wasproved by the fact that no separation occurred during severe forming,such as by Erichson bulge testing, by cupping, by pulling in tension torupture, and by bending with the cladding either in tension orcompression; and no bond blistering during thermal treatments of thecomposite, as, for example, high temperature annealing subsequent tocold rolling.

Further, the cladding and core materials were found to be compatiblegalvanically. The cladding provided cathodic protection for the corematerial.

Example 2.Core alloy 5086-cladding alloy 5557 In a manner after Example1 a composite was prepared from the above core and cladding alloys. Theresultant composite had characteristics similar to that of Example 1,with the following specific values found:

Yield strength p.s.i. 17,00020,000 Tensile strength p.s.i. 36,00038,000Elongation in two inches percent.. 21-27 Example 3.Core alloyS083-cladding alloy 5457 In a manner after Example 1 a composite wasprepared from the above core and cladding alloys. The resultantcomposite had characteristics similar to that of Example 1, with thefollowing specific values found:

Yield strength p.s.i. 21,000 Tensile strength p.s.i. 42,000 Elongationin two inches percent 22 Example 4.Core alloy 5083cladding alloy 5557 Ina manner after Example 1 a composite was prepared from the above coreand cladding alloys. The resultant had characteristics similar to thatof Example 1, with the following specific values found:

Yield strength p.s.i 21,000 Tensile strength p.s.i 42,000 Elongation intwo inches percent 22 Example 5.Comparative Example 1 was repeated, withthe exception that prior to hot rolling the composite was welded alongthe entire lead end, sides and tail, with no vent being provided in thetail end. Separation of the cladding and core materials occurred uponthe materials exiting from the rolls.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

1. The method of forming a composite which comprises:

providing a core material containing from 2 to 10% magnesium, balanceessentially aluminum;

cleaning said core, forming an assembly by superimposing thereon adissimilar cleaned cladding containing up to 2.5% magnesium, balanceessentially aluminum;

peripherally integrating said assembly by fusion welding, leaving anunintegrating peripheral portion in the posterior portion of saidassembly;

hot rolling said assembly at a temperature of from 450 to 950 E, therebyventing the air at the interface; and

integrating said core and cladding to form a composite wherein thecladding is from 5 to 20% of the thickness of the composite.

2. A method according to claim 1 wherein said clad ding contains from0.01 to 2.5 magnesium, up to 0.3% copper, up to 0.45% manganese, up to0.17% iron, and up to 0.12% silicon.

3. A method according to claim 1 wherein said core material containsfrom 0.15 to 1.0% manganese, and from 0.05 to 0.30% chromium.

4. A method according to claim 1 wherein said core alloy is alloy 5086and said cladding is alloy 5457.

5. A method according to claim 1 wherein said core alloy is alloy 5086and said cladding is alloy 5557.

6. A method according to claim 1 wherein said core alloy is alloy 5083and said cladding is alloy 5457.

References Cited UNITED STATES PATENTS 2,468,206 4/1949 Keene 29472.32,937,435 5/1960 Brenner 29196.2 3,001,059 9/1961 Jones 29471.53,150,445 9/1964 Butt 29471.5 3,228,103 1/1966 Shewmon 29471.5

FOREIGN PATENTS 618,129 4/ 1961 Canada.

OTHER REFERENCES Alcoa Aluminum Handbook, published by Aluminum Companyof America, 1962 (pp. 44-48).

JOHN F. CAMPBELL, Primary Examiner. R. F. DROPKIN, Assistant Examiner.

US. Cl. X.R. 29-488, 497.5, 498, 504, 197.5

1. THE METHOD OF FORMING A COMPOSITE WHICH COMPRISES: PROVIDING A COREMATERIAL CONTAINING FROM 2 TO 10% MAGNESIUM, BALANCE ESSENTIALLYALUMINUM; CLEANING SAID CORE, FORMING AN ASSEMBLY BY SUPERIMPOSINGTHEREON A DISSIMILAR CLEANED CLADDING CONTAINING UP TO 2.5% MAGNESIUM,BALANCE ESSENTIALLY ALUMINUM; PERIPHERALLY INTEGRATING SAID ASSEMBLY BYFUSION-WELDING, LEAVING AN UNINTERGRATING PERIPHERAL PORTION IN THEPOSTERIOR PORTION OF SAID ASSEMBLY; HOT ROLLING SAID ASSEMBLY AT ATEMPERATURE OF FROM 450 TO 950*F., THEREBY VENTING THE AIR AT THEINTERFACE; AND INTEGRATING SAID CORE AND CLADDING TO FORM A COMPOSITEWHEREIN THE CLADDING IS FROM 5 TO 20% OF THE THICKNESS OF THE COMPOSITE.